Tables for pipe support spacing

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Tables for pipe support spacing

Tables for pipe support spacing

Are there published tables for the maximum unsupported run of pipe per given pipe size??? I can calculate the maximun stress values but was wondering if there are standard tables for support apacing based on stress and deflection.

Neither are available without forking out cash. Since you are a valued guest of this forum, I'd be happy to email you pdf forms of these tables. I can't copy the whole publication for copyright issues, etc., but I don't see a problem with providing just the table info. (hopefully these folks don't either).

RE: Tables for pipe support spacing

You're going to want to be careful with a 30" line, particularly if it is liquid full. Most of these span tables are based on bending stress and deflection. When you gets to pipes that large, local/horn stresses at the support location become a bigger concern that need to be address by the support design (typically a saddle). A common reference in this area is the work of L.P. Zick on the design of support saddles for horizontal vessels. I'm sure others here can suggest more references.

I haven't looked at Isthill's reference since I've not really worked with Power Piping, but I would imagine it probably makes some note of these issues.

RE: Tables for pipe support spacing

I have calculated the pipe stresses for the given spans in the MSS publication and found that the stresses are usually less than the allowables found in either B31.3 or B31.8. So the problem then becomes how much deflection is acceptable.

I might add that I do not think that the MSS publication includes 30" pipe but I could be wrong as it has been some time since I looked at it.

Does anyone have any deflection guidelines for services other than steam?

RE: Tables for pipe support spacing

Tankman650:ITT- Grinnell publication "Pipng Design and Engineering" have a table of suggested pipe hanger spacing of Carbon Steel pipe filled with water based on a bending and shear stess not exceeding 1500psi and a deflection between hangers not to exceed .1". as follows:

Nom. Size Span1 71.5 92 102.5 113 123.5 134 145 166 178 1910 2212 2314 2516 2718 2820 3024 3226, 28 3330, 32 3434, 36 3542 36I have found this to be a good basic guide. These spans are for straight pipe only. Bends, valves and other added loadas will effect the span. If there is any question as to the span a stress analysis should be done. CaesarII is an excellend stress program which is user friendly and easy to use. A 50 run version can be purchased for about $700. Look on the web.

RE: Tables for pipe support spacing

Be aware also that the B31.1 table is fairly conservative, particularly for smaller lines. For B31.3 refinery piping, most engineering companies that I know of allow down to 2" diameter piping to span 20ft in standard pipe rack bays. With that table, you need to have a minimum of 10" piping in your pipe racks.

Also, typical deflection criteria is 1/2"-5/8" for ISBL lines. This span translates to a minimum natural frequency of 4Hz which is a suggested minimum to keep your pipe spans from galloping like the Tacoma Narrows Bridge.

Edward L. KleinPipe Stress EngineerHouston, Texas

All opinions expressed here are my own and not my company's.

RE: Tables for pipe support spacing

Previous replies and responses to the pipe span question have not considered siesmic forces. If the location of the piping installation is in an area with earthquake history, this may lead the engineer or officials to make certain site-specific recommendations or design requirements.

RE: Tables for pipe support spacing

All horizontal pipe support equations that I have seen are based on the fundamental beam equations found in strength of material. Bending stress and deflection are the two main criteria. ASME piping code for power boilers also requests the additional load of water filling the pipes.

RE: Tables for pipe support spacing

I did confirm - the 4Hz criteria comes from the Kellogg Design of Piping Systems. In general, if your piping system sags less than 5/8" between supports, the natural frequency will be above 4Hz. You want it above this to avoid exciting a resonance with the wind blowing across it. (Tacoma Narrows Bridge, anyone?)

RE: Tables for pipe support spacing

I gladly would if I could, as there is a lot of good information in that book. I've written the publisher to let them know there's interest in a new printing, but they indicate they've no plans to reprint it at this time.

They show up on Ebay about once or twice a year and never go for less that $50.

For now, I have to rely on the library of my boss, Noble Stewart, who thankfully has managed to amass copies of just about everything in his career.

In fact, I'm currently borrowing a 30 year old catalog for a spring manufacturer that went out of business about 25 years ago to evaluate a piping system with some existing springs. It's amazing how much information is simply dissapearing, save for a few pockets that are keeping it alive.

Edward L. KleinPipe Stress EngineerHouston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

RE: Tables for pipe support spacing

AARGH! Not good news. What about the 25-years-and-the-copyright-expires/public domain thing?

The web is a good thing for manufacturer's catalogs in most cases. A major excpetion to this is old equipment (as you related) which lots of owners still have in operation, forcing us to keep paper copies around. Worthington pumps is one good example.

Guess I will have to watch ebay... well I'll buy you lunch anyway next time I'm down there, how bout that. Thanks Ed.

RE: Tables for pipe support spacing

I am surprised that nobody mentioned that the classic "span length tables" always include warnings (in fine print) that these recommended spans are for simply supported piping (no moment connections) and do not address the presence of concentrated loads (valves, strainers, etc). Also, changes in direction add some complexity to the equation.

I wonder if ye olde Grinnell publication on pipe support design is still available through Anvil. EPRI members should look on the EPRI website for a PowerPoint presentation that some olde codger prepared.

Regards, John.

RE: Tables for pipe support spacing

JohnBreen, Good observations and post. Another thing a lot of people forget is that the pipe span tables are created in many instances for "ambient" piping systems and are then applied irrespective of the pipe temperature. Spans should be modified if high temperature lines are to be considered. I know that high temp lines are nearly always stressed out but the designer needs to account for the temperature in assessing spans. As you say a lot of the span tables are based on simple supports but in reality the end conditions are never simple and there is always some rotational restraint.

RE: Tables for pipe support spacing

I have a 500kb PDF file that has six pages scanned from the old Kellogg book on the span calcs. I'll see about finding a place to put it and then I'll post a link to it. Obviously, I can't scan the whole book, but this much ought to at least be able to spread the understanding on this topic. Judging from the interest this thread keeps getting, it is quite obviously needed. Stay tuned.

Edward L. KleinPipe Stress EngineerHouston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

RE: Tables for pipe support spacing

Certain pipe industries utilize normalized tabulations that yield support spacings "closer than" the ANSI B31 or Kellog spans due to the cumulative effects of low points in specific pipes that are deliberately sloped. Normally these slopes are effected to ensure that flow variances do not result in unantipated flow phenomena, for example: Condensate induced shock when re-applying steam to what should be a dry header; pumped recirculaion return lines on many central refrigeration systems, where not only could there be a charge management problem due to sags accumulating liquid but also a temperature induced stress when the pressure is reduced on a pipeline carrying relative warm vapor and pockets of liquid at low points.

The practicalities of supporting even that slope over 1000 or so feet of pipe leads the refrigeration industry to use 1/240 as a practical, and manageable, design slope....With the Deflection in a 10-foot support span headed for 5/8" per some of the mentioned tabular data, the accumulation problem, with its inclemencies, is not solved by the "field applied" slope.

As well, above and beyond the "stress" considerations: At the lower and lower temperatures that "normal" end-user industries are requiring of large compression systems: the Rigidity and (nil) Ductility Transition Temperatures become a very real concern and the incorporation of conventinal "expansion loops" exacerbates the problem...

So investigations of the rupture of a low temperature 2-phase pipe often establish the immediate conditions as: Bottom of pipe broke while the pressure was reducing; the flow was near its lowest; in the midst of a long stright run; halfway between supports; where its most proximate area of support is at the immediate point of contact, a deformable or otherwise, flexible insulation material. Conclusion: Minimal localized stress at the supports, minimal hoop and axial stress, minimal momentum forces due to changes in flow direction, minmal bending moment, on tensile side of pipe...Pipe still broke.

RE: Tables for pipe support spacing

Here goes my efforts to explain (hope isn’t too long)-A little more info on the “span charts”:Looking at Navco, p150, the Navco suggested support spacing is based on 2300 psi bending stress. MSS-SP-69, p8, is based on 1,500 psi, although I can’t seem to quickly find it in the text. There are many “company” standard span charts also. Anyway, most tables have notes and qualifications although I’ve seen some “company” charts copy other sources and leave this critical information out. These notes may include items like the following:*The pipe is assumed to have standard wall thickness with insulation,*No concentrated loads present such as valves,*There are no changes of direction in the spans, *Spans are assumed to run in the horizontal plane,*The maximum deflection of the span under load is limited to 0.1”, and *The stress intensification factors of components are not considered.

I am almost certain that SP-69 was generated using allowable stress values from the power piping code. The following is an attempt to show how the span tables might have been generated:

Select a low allowable stress value, e.g., 1,500 psi (Sall(weight)/i), for the combined bending and shear value, such that a sufficient factor of safety is provided, and allowing the standard span chart to be applied to a wide range of piping systems:

An example of a critical type system might look like:Assuming B31.1 and A181 materialP = 2600 psigT = 1060FSh = 6,000 psiLet PD/4t = 3000 psi (approx)This leaves 3,000 psi. A system design of this type will utilize lower SIFs, say in the range of 1-2, so,3,000/2 = 1,500 psiNote that the wall thicknesses will be greater and the fabrication control improved resulting in the lower SIFs.

I’ve left out several steps to save some space, because I think that the most important thing to know when using a standard span table is generally how it was constructed, and what simplifying assumptions were made.

Also related is a calculation (ref. Hick’s) to determine the minimum slope of a pipe to ensure complete draining. On the one hand it is a little conservative since emptying is not considered, but there are other factors that can negate its conservatism. If interest, I can post that relation also. . .

RE: Tables for pipe support spacing

By the way, another good source for span charts is from Chapter B-4, Stress Analysis of Piping Systems, Piping Handbook, 7th edition. This has charts for various sizes of pipe (standard schedules), both empty and water full. It also has a neat deflection chart.

As most everybody has observed, these charts are good "estimates" or guidelines - given the assumptions they are based on......

For slope considerations, there is a good article available on the web titled "DETERMINATION OF THE OPTIMAL PIPE SUPPORT SPANS FOR GEOTHERMAL PIPELINES. If you just type in the first four words of the title in GOOGLE, you'll find it. Sectin 5.3 talks about sag and drainage.

2. Compute the pipe slope required by the spanto prevent pocketing of water of condensate at the low point in the pipe, the pipe must be pitched so that the outlet is lower than the lowest point in the span. when the pipe has no concentrated lods-such as valves, cross connections, or meters-the deflection of the pipe is y in = 22.5wl^4/(EI), wehre w = weight of the pipe and its contents, lb/ft; l = distance between hangers, ft; E = modulous of elasticity of pipe, lb/in^2 = 30 x 10^6 for steel; I = moment of inertia of the pipe, in^4. with the deflection y known, the pipe slope, expressed as 1 in per G ft of pipe length, is 1 in per G ft = l(lower case L)/4y. Thus, a pipe slope of 1 in in 4.53 ft is necessary to prevent pocketing of the water when the hanger span is 47.4 ft. with this slope, the outlet of teh pipe would be 47.4/4.53 = 10.45 in below the outlet.

Personally, on the one hand I think this is a bit conservative since the deflection decreases as the pipe empties. However, it may not be so conservative when some construction practices, creep, and so on are considered.

RE: Tables for pipe support spacing

First of all, each of the above response above are very accurate and well taught.

The best rule of thumb for hanger spacing for pipe is the pipe diameter in feet plus 10. Example: a 3" pipe would require a support every 3'+10" = 13'-0. Use that and you should be fine for small diameter pipes 1/2" - 12".

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